Measuring angular velocity or angular rate (absolute value of an angular velocity vector) with a vibrating sensor of angular velocity is known to be a simple and reliable concept. In a vibrating sensor of angular velocity, a primary motion of vibrating mass/es is produced and maintained in the sensor. The motion to be measured is then detected as deviation from the primary motion.
International patent publication WO2010/100333 A1 discloses a micro-mechanical sensor of angular velocity comprising two masses coupled in the direction of a common axis.
In a MEMS gyroscope, mechanical oscillation is used as the primary movement, referred also to as the primary motion or the primary mode. When an oscillating gyroscope is subjected to an angular motion orthogonal to the direction of the primary motion, an undulating Coriolis force results. This creates a secondary oscillation, also referred to as the secondary motion, the detection motion, the sense mode or the secondary mode, which is orthogonal to the primary motion and/or to the axis of the angular motion, and at the frequency of the primary oscillation. The amplitude of this coupled oscillation can be used as the measure of the angular rate, i.e. the absolute value of angular velocity.
In a gyroscope device, combination of multiple moving masses may cause total angular momentum in addition to total linear momentum, both of which may cause some problems in the gyroscope device. For example, non-zero total momentum may cause instability of rate offset, rate signal noise, susceptibility to and/or interference with external mechanical shock and vibration.